Hard soap/alcohol gel sticks make desirable application vehicles for cosmetics and deodorants because they tend to exhibit good skin glide and low visible residue. Unfortunately, the acidic antiperspirant actives interfere with the gel structure and render it less cosmetically desirable.
Acceptable cosmetic and deodorant gel sticks may, however, be made using dibenzylidene sorbitol (DBS) and certain of its derivatives as the gelling agent, instead of soap. DBS gel sticks are disclosed in U.S. Pat. No. 4,154,816, Roehl et al., issued May 15, 1979; U.S. Pat. No. 4,518,582, Schamper et al., issued May 21, 1985; U.S. Pat. No. 4,743,444, McCall, issued May 10, 1988; and U.S. Pat. No. 4,816,261, Luebbe et al., issued Mar. 28, 1989; all incorporated herein by reference. Japanese Published Application 64-62377, Kao, published Mar. 8, 1989, describes fluorinated dibenzylidene polyhydric alcohol derivatives, including sorbitols, as effective gelling agents for cosmetic compositions containing a wide range of organic solvents.
Specific methods for making DBS are disclosed in U.S. Pat. No. 4,429,140, Murai et al., issued Jan. 31, 1984, and European Patent Application 0286522, Salome et al., published Jan. 12, 1988; both incorporated herein by reference. Murai et al. discloses a method for producing DBS and its derivatives using substituted or unsubstituted benzaldehyde and alkyl acetal derivatives of benzaldehyde, sorbitol, an acid catalyst, a hydrophobic solvent reaction medium (e.g., cyclohexanes, carbon tetrahalides, aromatic hydrocarbons, hydrocarbon halides, and nitro compounds), and a hydrophilic organic polar solvent (e.g., alcohols and glycol ethers). The reaction is a dehydration/condensation process in which the water and hydrophobic solvent azeotrope is continuously removed. The presence of sufficient amounts of the hydrophobic solvent is necessary for the DBS to precipitate out. Furthermore, the hydrophilic solvent solubilizes both the sorbitol and aldehyde, which is necessary for the reaction to proceed. In this process the hydrophilic and hydrophobic solvents must be carefully balanced, making it rather complex and costly. Furthermore, a complicated recycling process for the hydrophobic solvent is disclosed therein.
U.S. Pat. No. 4,131,612, Uchiyama, issued Dec. 26, 1978, discloses the use of lower aliphatic alcohols, such as methanol, for purifying crude DBS made by a process similar to Murai et al. (i.e., where cyclohexane is used as the solvent medium). In this purification process, a solution of crude DBS and methanol is heated to at least 50.degree. C. to remove mono- and tribenzylidene-D-sorbitols which account for up to 7% by weight of the crude DBS. However, as is the case in Murai et al., using cyclohexane, a hydrophobic organic solvent, makes the process quite complicated.
An alternative process to Murai et al. for producing DBS is disclosed in European Patent Application No. 0286522, Salome et al., published Oct. 12, 1988. Salome et al., like the references above, utilizes an acetalization reaction catalyzed by an argylsulfonic acid to yield, upon successive dehydration, dibenzylidene-D-sorbitol compounds, including the para-chlorine derivatives. This process utilizes an aqueous medium instead of the hydrophobic organic solvent eliminating the steps surrounding reclamation of the solvent reaction medium as taught by Murai et al.. Furthermore, the hydrophilic organic co-solvent is eliminated making the reaction relatively simple.
The Salome et al. process, however, requires neutralization of the residual acid catalyst. Omission of the neutralization step results in formation of DBS isomers which will not gel. Neutralization, however, leaves alkaline impurities in the product which causes chemical reactions among other ingredients in the stick formulation, thereby depleting the gellant. In addition to the neutralization problem, halogenated, specifically chlorinated, DBS derivatives are not preferred for manufacturing using the Salome et al. process due to the low yield of DBS and the high yield of monobenzylidene-D-sorbitol compound.
While the reaction parameters of the present invention, such as the molar ratios of aromatic aldehyde to D-sorbitol, the use of aryl sulfonic acid catalysts, and the molar ratio of acid and aromatic aldehyde, are similar to those taught in the art, the process of the present invention utilizes a C.sub.1 -C.sub.3 aliphatic alcohol, as opposed to a hydrophobic solvent or water, as the reaction medium. Using the alcohol instead of a dual solvent as in Murai et al. simplifies the reaction. Subsequent washing with the alcohol effectively removes the acid catalyst without neutralization as taught by Salome et al., eliminating alkaline impurities in the product. Furthermore, residual alcohol is quickly removed from the product of the present invention by simple means, such as drying in air or in an oven, whereas the removal of the water from the product of the Salome et al. process, is more difficult. In addition, eliminating water from gel sticks gene-rally results in better cosmetics.
The present process, therefore, produces, in a simple manner, dibenzylidene sorbitol compounds, and particularly meta-substituted halogenated derivatives, which have better purity when compared to materials made by processes taught in the art. Better purity means that the DBS compounds are essentially free of water, hydrophobic organic solvents (such as cyclohexane), undesirable mono- and tribenzylidene sorbitol compounds, acid catalyst, and alkaline impurities. Products made by this process have superior properties when used as gelling agents in antiperspirant stick compositions.
All parts and percentages given herein are by weight unless otherwise indicated.